Telephone communication apparatus has now become a means requisite to the modern people for communication. Only through telephone communication apparatus the transmission of information, market report, and commercial transactions can be made simply, rapidly and efficiently. Since telephone communication apparatus has now become so important in our daily life, a telephone communication local line subscriber may suffer a loss if the telephone communication apparatus fails to work or the line is illegally connected by somebody else. The present invention is designed to provide a solution to said problems, that is, to provide a multipurpose subscriber local line monitoring device to monitor the operation of telephone apparatus so as to prevent against illegal connection of the line.